1. Field of the Invention
The present invention relates to the technology of polishing with a high surface precision or grinding a curved surface such as a spherical or aspherical surface.
2. Related Background Art
(1) For the purpose of polishing an object with a curved surface, for example an optical component such as a lens, Japanese Laid-open Patent No. 1147/1984 discloses an apparatus shown in FIGS. 1A and 1B. As shown in these drawings, a table 7 placed on a bed 6 is provided with an inclining unit 9 for rotating a shaft 8. Said table 7 and said inclining unit 9 are driven by instruction signals from a numerical control unit 10, whereby the table 7 is moved in the direction of the X-axis while the shaft 8 is rotated by the inclining unit 9. At an end of the shaft 8 opposite to the inclining unit 9 there is provided a work rotating unit 13 composed of a motor All and a rotating table 12, in which the rotation of the motor All is transmitted to said table 12 to rotate a work 4 mounted on said table 12. A column 14 is connected to the bed 6, and a polishing head 3 is slidably mounted on a guide rail 15 supported by said column 14. The polishing head 3 is rendered movable in the direction of Z-axis by an electric-hydraulic servo mechanism composed of a controller 16, a hydraulic control unit 17 and a hydraulic cylinder 18, thereby applying a tool 19 such as a grinding stone or an elastic member to the work 4 under a predetermined polishing pressure. The polishing head 3 is provided therein with a motor B20, thereby rotating the tool 19.
In the following there will be an explanation of the polishing apparatus explained above. FIG. 1B is a schematic view showing the function of said apparatus.
Input data is given to the controller 16 from a data setter 22 mounted on an operation console 21. Said input data is composed of a function F(x) defining a curved surface 5 to be polished, polishing ranges x.sub.1, x.sub.2 of said curved surface 5, a relative speed between the tool 19 and the work 4, a number n of cycles to be explained later, an ascending or descending distance h of the tool 19, an amount .DELTA.x of movement. In FIG. 1B, in the initial setting of the work 4 and the polishing head 3, the angle .theta. and the tool position ( are both at zero. When the polishing operation is started in this state, the controller 16 executes a calculation according to the equation (1) with a radial position x.sub.1 on the curved surface 5, and the result of calculation is transferred to the numerical control unit 10 whereby the inclining unit 9 shown in FIG. 1A inclines the work rotating unit 13 by an angle .theta. and the table 7 is moved to the tool position l. Also the controller 16 executes a calculation according to the equation (2) to determine the work rotating speed N.sub.w and activates the motor All to rotate the work 4 while rotating the motor B20 in synchronization, thereby matching rotating speed of the tool 19 with that of the work 4. In such state the controller 16 activates the hydraulic control unit 17 to lower the polishing head 3. Whereby the tool 19 is brought into contact with the curved surface 5 to achieve polishing operation, under a constant polishing pressure of the tool 19 on the surface 5. After the work 4 rotates by a predetermined number n of cycles at the radial position x.sub.1 on the curved surface 5, the polishing head 3 is elevated by a height h in the Z-direction in response to an instruction signal from the controller 16. Then the amount of movement .DELTA.x of the input data is added to x.sub.1 whereby the controller 16 renews the radial position on the surface 5 to (x+.DELTA.x) and repeats the operation in a similar manner as in the radial position x.sub.1. In this manner the controller 16 moves the radial position x on the curved surface 5 in the polishing range from x.sub.1 to x.sub.2 whereby the processed surface 5 is efficiently and automatically polished by the tool 19 in uniform manner.
(2) Optical components, for example photographing lenses for use in a camera, have spherical and aspherical surfaces, and require high precision for surface smoothness. Also the requirement for the precision of products with respect to the design value of the spherical or aspherical surface is strict. In case of an aspherical lens, manufacturing precision can be achieved if the degree of asphericity is small, but, if it becomes larger, precision is very difficult to maintain. When a particular glass material is finished to a preliminary surface coarseness and particular tool and particular polishing conditions (abrasive, polishing pressure, polishing speed etc.) are selected, it is already known that the amount to be abraded in such system is proportional to the polishing time, and this relationship is utilized in the computer controlled polishing for controlling the work and the tool.
Among such apparatus for controlling the function of work and tool with a computer, there are already known:
(2-1) apparatus in which an aspherical work piece is rotated, as disclosed in the U.S. Pat. Nos. 3,566,544, 3,564,776 and 3,769,762;
(2-2) apparatus in which a work piece is rotated while a tool is moved in the radial direction of the work, as disclosed in the U.S. Pat. Nos. 3,566,544 and 3,564,776; and
(2-3) apparatus in which a work piece is fixed while a tool performs a scanning motion in the X- and Y-directions, as disclosed in the U.S. Pat. Nos. 3,587,195, 3,589,078 and 3,676,960.